Food that is heated in a microwave oven does not appear to couple well with the microwave energy in certain ovens. This causes less heating and poorer cooking results in certain ovens. For example, popcorn may not pop very well in some ovens. In virtually all home microwave ovens now manufactured, food is supported on a ceramic or glass shelf or false floor that is spaced an inch or two above the metal oven floor. The distance of the false floor above the metal floor of the oven varies from one manufacturer to another. In the course of developing the present invention, it was found that a standardized package of food was subjected to different heating conditions in different ovens. It was also determined that the amount of heating, i.e., the efficiency with which heat is induced into the food, appeared to be influenced by the height of the false floor from the microwave reflective metal floor of the oven.
The major objective of the present invention is to provide a compact, collapsible device that will asure more uniform heating of foods in a variety of microwave ovens of differing dimensions and will improve, speed up and generally facilitate the heating of foods but which is formed entirely from flexible or semiflexible packaging materials adapted to be withdrawn from a roll, printed, cut and formed like a conventional package so that little if anything is added to the cost of an ordinary package.
A number of devices have been previously proposed to assist in the heating of foods in a microwave oven. For example, U.S. Pat. No. 4,013,798 describes a box which forms a shield supporting a metal tray above a reflective bottom layer. However, the box extends over the top of the food and prevents microwave energy from reaching it from the top. The shielding effect of the box together with the loss of microwave energy through holes in the bottom layer tend to prevent microwave energy from reaching the food. Microwave energy is reflected away from both the top and bottom of the surrounding box.
U.S. Pat. Nos. 2,612,596 and 3,835,280 both propose microwave heating devices composed of blocks of dielectric material, e.g., plastic blocks having a sheet of metal beneath them. The blocks are bulky and plastic relatively expensive due to the large amount of plastic resin needed. More importantly the blocks of dielectric material deemed necessary for operation take up a great amount of space rendering the devices unsuited for use as a disposable unit in a light weight package.
In the development of the present invention it was found that aluminum foil reflectors bonded to paper or paperboard would arc, scorch or burn the paper. This was very objectionable to users especially when the paperboard was badly scorched, blackened or was smoking hot when the oven was opened.
A variety of prepared foods are now sold in the supermarket within a package specifically designed to contain the food that is heated in a microwave oven. To be sucessful, these packages must be composed of inexpensive, flexible or semiflexible packaging material such as paper, paperboard or foil capable of passing through conventional paper and paperboard converting equipment such as printers, sheet cutters and the like. One important object of the invention is to provide a reflective support to improve the heating of such packaged foods without adding much to their cost and to do so without burning, scorching or blackening the support or the food.